/* Copyright 2017 The TensorFlow Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#ifndef TENSORFLOW_COMPILER_XLA_SERVICE_TUPLE_SIMPLIFIER_H_
#define TENSORFLOW_COMPILER_XLA_SERVICE_TUPLE_SIMPLIFIER_H_

#include <utility>

#include "tensorflow/compiler/xla/hlo/ir/hlo_instruction.h"
#include "tensorflow/compiler/xla/hlo/ir/hlo_module.h"
#include "tensorflow/compiler/xla/service/hlo_pass_interface.h"

namespace xla {

// A pass which simplifies patterns of Tuple and GetTupleElement instructions in
// the module.
class TupleSimplifier : public HloModulePass {
 public:
  TupleSimplifier() : TupleSimplifier(/*exclude_entry_computation=*/false) {}
  explicit TupleSimplifier(bool exclude_entry_computation);
  ~TupleSimplifier() override {}
  absl::string_view name() const override { return "tuple-simplifier"; }

  // Run tuple simplification on the given computation. Returns whether the
  // computation was changed.
  using HloPassInterface::Run;
  using HloPassInterface::RunOnModuleGroup;
  StatusOr<bool> Run(
      HloModule* module,
      const absl::flat_hash_set<absl::string_view>& execution_threads) override;

 private:
  // When set, this pipeline stage will perform optimization of all computations
  // apart from the module's entry computation. This is used by Graphcore's
  // backend.
  bool exclude_entry_computation_;

  // Collapse the following structure into just 'Tuple-shaped Op':
  //
  //   Tuple-shaped Op
  //         |
  //   +-----+-----+
  //   |     |     |
  //  GTE   GTE   GTE
  //   |     |     |
  //   +-----+-----+
  //         |
  //       Tuple
  //
  StatusOr<bool> RemoveWholeTuple(HloInstruction* tuple);
};

}  // namespace xla

#endif  // TENSORFLOW_COMPILER_XLA_SERVICE_TUPLE_SIMPLIFIER_H_
